A total of 66 cases of thymoma(57 surgically resected cases and 9 incisional biopsy cases) were reviewed with an attempt to correlate pathomorphologic features and clinical presentations. Criteria of benign or invasive thymoma were primarily determined by operative clinical and pathologic findings. Of them, 21 cases were invasive thymomas. The mean age of patients at the time of surgery was 47 years and it occurred largely in the sixth decade. Myasthenia gravis was accompanied in 29 cases(43%). One patient died during folow-up period, and five of the remainder suffered from recurrence. Microscopically, mixed type was the most common one(33 cases), being followed by predominantly epithelial type(17 cases) and predominantly lymphocytic type(16 cases). Thirty four cases of thymomas were cortical type, 29 mixed type, and the remaining 3 medullary type. None of the histologic type were significantly correlated with tumor invasiveness, Myasthenia gravis was more frequently associated with mixed and cortical type, respectively.